Advancing scientific understanding

To strengthen the scientific understanding of the physical basis for win-win options for development, air quality and climate change, the Mitigation of Air Pollution and Greenhouse Gases (MAG) Program contributed to a number of scientific assessments that were finalized in 2013, including a major assessment on black carbon.

Coal in pot

The landmark "Bounding BC" assessment [1] managed to significantly reduce uncertainties about the direct radiative forcing of black carbon, and reinforced the critical importance of simultaneously considering the impacts of all co-emitted species - a crucial aspect emerging from MAG’s systems perspective.

MAG also contributed recent regional emission trends of short-lived climate pollutants to the Fifth Assessment Report of the IPCC [2], and of non-CO2 greenhouse gas emissions and mitigation potentials to the N2O Assessment of the United Nations Environment Programme (UNEP) [3].

Although the scientific understanding of the latter is less developed, it is clear that cloud formation is strongly influenced by very small particles (typically, less than 100 nanometers), which are often represented by the number of particle concentrations. However, these smallest particles constitute only a minor share of total PM mass concentrations (e.g., of PM2.5, particles smaller than 2.5 micrometers), which is more relevant for association with health impacts.

Emission trends and mitigation potentials for particle numbers could be rather different from those for particle mass, which is usually addressed in emission control strategies. In cooperation with the University of Helsinki, MAG developed a new component of its GAINS model that assesses present and future emissions of particle numbers, and quantifies the co-control of this quantity with emission control strategies that aim at other substances and particle properties [4], [5].